.\"     $NetBSD: cred.9,v 1.4 2003/01/25 19:27:43 kleink Exp $
.\"
.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Gregory McGarry.
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.Dd January 25, 2003
.Dt CRED 9
.Os
.Sh NAME
.Nm cred ,
.Nm crcopy ,
.Nm crcvt
.Nm crdup ,
.Nm crfree ,
.Nm crget ,
.Nm crhold ,
.Nd operations on user credentials
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/param.h\*[Gt]
.Fd #include \*[Lt]sys/ucred.h\*[Gt]
.Ft struct ucred *
.Fn crcopy "struct ucred *cr"
.Ft void
.Fn crcvt "struct ucred *cr" "const struct uucred *ucr"
.Ft struct ucred *
.Fn crdup "struct ucred *cr"
.Ft void
.Fn crfree "struct ucred *cr"
.Ft struct ucred *
.Fn crget "void"
.Ft void
.Fn crhold "struct ucred *cr"
.Sh DESCRIPTION
A process must have the appropriate user credentials for the kernel to
perform an operation on its behalf.
The user credentials are stored along with the process in the following
structure:
.Pp
.Bd -literal
struct ucred {
        u_int32_t       cr_ref;                 /* reference count */
        uid_t           cr_uid;                 /* effective user id */
        gid_t           cr_gid;                 /* effective group id */
        u_int32_t       cr_ngroups;             /* number of groups */
        gid_t           cr_groups[NGROUPS];     /* groups */
};
.Ed
.Pp
User credentials are controlled by the
.Xr group 5
and
.Xr passwd 5
files and manipulated using the
.Xr setregid 2 ,
.Xr setgid 2 ,
.Xr setegid 2 ,
.Xr setgroups 2 ,
and
.Xr getgroups 2
system calls.
.Pp
References to user credentials are maintained from many different data
structures, including processes, file descriptors and vnodes.
The ucred member
.Em cr_ref
reflects the number of references to the credentials.
.Sh FUNCTIONS
The following functions operate on user credentials:
.Pp
.Bl -tag -width compact
.It Fn crcopy "cr"
Allocate a new credentials structure and copy the contents from
credentials
.Fa cr
to the new one.
The old credentials
.Fa cr
are freed.
The reference count on the returned credentials is guaranteed to be one.
.It Fn crcvt "cr" "ucr"
Convert from userland credentials
.Fa ucr
to kernel credentials
.Fa cr .
.It Fn crdup "cr"
Allocate a new credentials structure and copy the contents from
credentials
.Fa cr
to the new one.
The old credentials
.Fa cr
remain unchanged.
The reference count on the returned credentials is guaranteed to be one.
.It Fn crfree "cr"
Decrement the reference count on credentials
.Fa cr .
If the reference count drops to zero, then the credentials are freed.
.It Fn crget "void"
Allocate and return zeroed credentials.
.It Fn crhold "cr"
Increment the reference count on credentials
.Fa cr .
.El
.Sh SEE ALSO
.Xr suser 9
.Sh BUGS
User credentials are sometimes allocated using
.Xr MALLOC 9
and sometimes using the
.Xr pool 9
facility.
This cannot be right.